A digital camera or video recorder employs one or more optical lenses to form a real image of an object onto a sensor. This sensor is generally a pixilated electro-optical device that outputs an electrical response to the real image formed onto the sensor. The electrical response can be manipulated to reform the real image on a digital optical display, such as a liquid crystal display (LCD). Technological advancements have enabled fabrication of smaller-sized sensors and optical components, thus, digital cameras and video recorders have been integrated into more and more consumer devices.
The use of digital imaging sensors and micro optics for cameras and video recorders has made the continuing miniaturization of these devices possible. As a result, camera modules have been integrated into small electronic devices, including hand-held devices such as cell phones, smart-phones and personal digital assistants (PDAs), computing devices such as laptops, net-books and desktop computers, display devices such as televisions, monitors and graphics displays, hidden or conspicuous surveillance equipment, and so forth. Improvements in image sensors have provided high resolution image detectors utilizing micro-scale pixilation, and at high signal to noise ratio and increasingly lower cost.
Any lens design should address the need to increase the Depth of Field (DoF) on the one hand and should enable the capture of an image under non-ideal lighting conditions, such as interior residential lighting conditions. These concerns can be difficult to satisfy with a standard lens system due to an effect known as “relative illumination”, which derives from variations in intensity according to the positions of digital pixel sensors in the field of view of the lens. In other words, non-uniform relative illumination generally results in a large disparity of light irradiating from different portions of a digital sensor. Thus, some areas of an image appear bright while other areas appear dim, reducing image quality.
Increased DoF is desirable in photography, as it allows for objects having a broader range of distances from a camera (both far and near) to appear in focus. For simple point-and-click camera modules without depth of focus adjustment, a lens design with a high DoF can greatly impact perceived camera quality. While distortion characteristics can be employed for altering DoF, high distortion can also cause poor relative illumination. Consequently, it would be desirable to have an optical system that can provide a distorted image for large DoF, as well as low variation in relative illumination across the field of view with no moving parts.